Hi,
Thanks for the feedback.
How often the takeoff thrust is reduced below climb thrust? Does it apply to short/medium haul, long-haul (2 and 4 engine aircraft)?
Once you get about 10% below max rated thrust, incremental reduction of engine wear is miniscule
About "10%" statement, just because it comes from a course
30 years ago, it does not mean it is right. You are taking it as absolute truth.
If you think it is absolute truth why Boeing and Airbus are not recommending or adopting this procedure (10%)? Boeing and Airbus have propulsion department with experts and engineers in this field.
Why airlines are not applying this procedure (10%)? Airlines have also propulsion department.
To my knowledge Boeing and Airbus are not engine leasing companies and they can't force airlines management (bean counters) to adopt reduced takeoff thrust (assumed and/or derate).
You don't have to decrease takeoff thrust to 40% all time. You can decrease thrust [B]up to 40% for certain conditions (40% is the limit). I think you can also use derate climb so the takeoff thrust is not reduced below climb thrust.
4 engine aircraft typically require a higher fraction of takeoff thrust in climb than twin-engine aircraft do. Climb operation may influence engine life on four-engine aircraft, but cruise altitude is reached earlier.
I think there is compromise between engine maintenance cost and the total fuel cost or the operating cost. Other factors can be considered noise abatement procedures, 4 engines aircraft vs 2 engine aircraft, medium haul vs long haul...etc.